Several types of pumps are especially useful for pumping fluids with minimal back-flow and that are amenable to miniaturization. An example is a gear pump. Another example is a piston pump. A third example is a variation of a gear pump in which the rotary pumping members have lobes that interdigitate with each other. Gear pumps and related pumps have experienced substantial acceptance in the art due to their comparatively small size, quiet operation, reliability, and cleanliness of operation with respect to the fluid being pumped. Gear pumps and related pumps also are advantageous for pumping fluids while keeping the fluids isolated from the external environment. This latter benefit has been further enhanced with the advent of magnetically coupled pump-drive mechanisms that have eliminated leak-prone hydraulic seals that otherwise would be required around pump-drive shafts.
Gear pumps have been adapted for use in many applications, including applications requiring extremely accurate delivery of a fluid to a point of use. Consequently, these pumps are widely used in medical devices and scientific instrumentation. Developments in many other areas of technology have generated new venues for accurate pumps and related fluid-delivery systems. Such applications include, for example, delivery of liquids in any of various automotive applications.
Automotive applications are demanding from technical, reliability, and environmental viewpoints. Technical demands include spatial constraints, ease of assembly and repair, and efficacy. Reliability demands include requirements for high durability, vibration-resistance, leak-resistance, maintenance of hydraulic prime, and long service life. Environmental demands include internal and external corrosion resistance, and ability to operate over a wide temperature range.
A typical automotive temperature range includes temperatures substantially below the freezing temperature of water and other dilute aqueous liquids. These temperatures can be experienced, for example, whenever an automobile is left out in freezing winter climate. A property that is characteristic of water and most aqueous solutions is that they tend to expand as they undergo a phase change from liquid to solid (ice). As is well known, household plumbing systems exposed to sub-freezing temperatures may develop static pressures produced by freeze-expansion that are sufficiently high to fracture pipes. Thus, these pressures can cause substantial damage to a pump that is coupled, in a primed condition, to a hydraulic circuit exposed to a sub-freezing temperature.
In view of the above, a simple solution is to add anti-freeze to the liquid or to constitute the liquid with sufficient solute to depress its freezing point. Unfortunately, changing the liquid in these ways changes the composition and possibly other important properties of the liquid, which may render the liquid ineffective for its intended purpose.
U.S. Pat. No. 8,323,008, (hereinafter the “'008 patent”), discloses pumps and pump heads comprising internal pressure-absorbing member(s) for alleviating at least some of a pressure increase occurring inside the pump head. The pressure-absorbing member is located inside the pump housing at a non-wearing location and contacts the fluid being pumped by the pump head. The pressure-absorbing member has a compliant property to exhibit a volumetric compression when subjected to a pressure increase in the fluid contacting the pressure-absorbing member. Pumps and pump heads as disclosed herein take a different approach to alleviating pressure inside the pump head.